Magnetic separation is well described in the literature. Jan Svoboda has reviewed the state of magnetic separation technology in “Magnetic Methods for the Treatment of Minerals”, Developments in Mineral Processing-8, ISBNO-44-42811-9, Elsevier, N.Y., 1987. Other general references include “Magnetic Separation”, Perry's Chemical Engineers' Handbook, McGraw-Hill, New York, 7th Edition, 1998, pp. 19-49 and John Oberteuffer and Ional Wechsler, “Magnetic Separation”, Kirk-Othmer Encyclopedia of Chemical Technology, 3rd edition, 1978, John Wiley & Sons, New York, Volume 15, pp. 708-732.
Several patents have issued dealing with vibrating matrix separators, namely, Frantz, in U.S. Pat. No. 2,074,085, that issued Mar. 16, 1937 describes a magnetic separator for fine powders. Frantz disclosed that separators based on the use of pulleys, rotors or belts are unable to make efficient separations when fed fine powders. Frantz's magnetic separator consists of an electromagnetic solenoid, a casing vessel and attractor screens as the matrix. In one embodiment of the invention, the matrix is vibrated by means of an eccentric weight fixed to a vertical shaft that is rotated by a motor.
Mechanical means is not the only method of vibrating the matrix; it is also possible by electromagnetic means. Kolm discloses in U.S. Pat. No. 3,567,026 that issued Mar. 2, 1971 and U.S. Pat. No. 3,676,337 that issued Jul. 11, 1972 the vibration of a fine steel wool matrix in a direct current solenoid separator using alternating current coils. Both Kolm patents describe a magnetic separator that includes one direct current coil and three alternating current coils. The direct current coil provides the background magnetic field that magnetizes the steel wool matrix to perform the main separation. The first alternating current coil is a demagnetizing coil to remove residual magnetization from the direct current coil. The other two alternating current coils create an eddy current to vibrate the steel wool matrix to shake loose retained components. A process is claimed for switching off the direct current field and applying the alternating current fields to flush magnetic fines out of the matrix. In addition to ferromagnetic wool, copper wool is optionally added to intensify the vibration. The eddy current is in the upper sonic range on the order of 18,000 to 20,000 cycles per second, and up. Perforated plates can optionally be used for flow distribution.
Although the Kolm patents are chiefly concerned with wet slurries, dry particulate removal is also contemplated from a stream such as fly ash contained in smoke from a power station.
Oder, in U.S. Pat. No. 4,087,358, that issued May 2, 1978 describes methods and apparatus for vibrating the matrix of a clay slurry magnetic separator to dislodge impurities during the flushing step of the operation. Vibratory hammering, shaking the matrix by auxiliary alternating current coils, and the use of high intensity sound, are suggested means of applying auxiliary mechanical forces to the matrix.
Wulff, in U.S. Pat. No. 2,372,665, that issued Mar. 20, 1945 describes a method of separating white cast iron powder into pearlite-rich and carbide-rich fractions by heating the mixed feed to 215° C. so that the carbide particles are above their Curie temperature and therefore not attracted to the magnetic field.
Collin in U.S. Pat. No. 4,000,060 that issued Dec. 28, 1976 describes a magnetic separator for hot powder mixtures. The separator consists of a drum roll separator with water-cooled permanent magnets. The non-magnetic rollers are set in a temperature controlled fluidized bed. The feed powder is fluidized with an inert gas such as nitrogen.
Inoue in U.S. Pat. No. 4,836,914, that issued Jun. 6, 1989, describes a process using a magnetic separator to remove iron particles from petroleum oil. The preferred temperature of operation is up to 400° C. This method has advantages over other treatment alternatives such as hydroxide treatment. It is especially advantageous for high viscosity oils.
Sometimes it is desirable to heat the matrix to aid in cleaning it between cycles. Dijkuis in U.S. Pat. No. 4,353,730 that issued on Oct. 5, 1982 describes a method for cleaning a magnetic separator matrix by heating a cleaning fluid above the Curie temperature of the matrix material in order to release magnetic fines.
There is disclosed an example of magnetic separation involving particles that are abrasive in U.S. Pat. No. 6,262,843, that issued on Jul. 24, 2001 to Wiesner in which it is taught how to remove impurities from the machining of semiconductor material wherein particles from saw blades or lapping plates can be magnetically separated from the cutting fluid used during the machining process for silicon.
Hazardous powders are those finely divided solids that are corrosive, flammable, toxic, or a combination of such hazards. Powders that are inherently hazardous must be completely contained inside the magnetic separator apparatus with a highly reliable leakage prevention design. Sometimes, hazardous dry powders are processed simultaneously with hazardous gases, vapors, or liquids. The hazardous fluids also contribute to the difficulty of operating a magnetic separator on such powders.
Confining such materials within the separator is very important. Small leaks of corrosive materials can result in corrosion failures of the containment vessel that lead to large, even catastrophic leaks. Corrosive and toxic materials can injure employees. Flammable materials can cause fires and explosions when they leak from a contained, inert environment to the atmosphere. Thus, the integrity and reliability of the containment system is very critical.
Additional problems are introduced when the separation is made at higher than ambient temperatures, higher than ambient pressures or when the solids are especially abrasive. High temperature operations make it impossible to use many polymer or elastomer materials that are available at lower temperatures. These materials might be the preferred material of construction for corrosion or abrasion resistance properties. At high temperatures, many polymers and elastomers are seriously weakened and thus fail in operation.
Pressure adds to this problem if the materials of construction are used for pressure containment or sealing. Loss of containment during operation above ambient pressure permits rapid leakage of process materials out of the separator to the atmosphere, thus creating a hazardous incident such as a fire or explosion. Similar hazards can be created inside the separator if it operates at vacuum so that air is drawn into the device on loss of containment. In addition to hazardous consequences on loss of containment, quality problems might also result on a process. An example would be a process where oxygen is a contaminant and the magnetic separator is operating under vacuum.
Abrasion of materials of construction of the apparatus is also a problem. The containment vessel can be eroded resulting in loss of containment. Seals are especially prone to containment failure, so avoidance of rotating mechanical seal faces or similar design features is critical. Detection of failures is also highly desirable.
There are many types of magnetic separators in industrial today. Several types of high gradient magnetic separators are known to the inventors herein. One is an enclosed belt separator including the MagnaCat® separator manufactured by Merrichem Company, located in Houston, Tex.
In U.S. Pat. No. 4,406,773, Hettinger et al. describe the use of a Sala high gradient carousel magnetic separator to separate samples of catalyst mixed with water. It is presumed that this separation of the slurry is made near ambient temperature. In U.S. Patent 5,147,527, Hettinger describes the use of a belt roller magnetic separator, especially the Eriez Magnetic Rare Earth Roll Permanent Magnetic Separator fitted with an electrostatically conductive belt. Separation is contrasted with an Eriez high gradient magnetic separator, but throughput of the high gradient magnetic separator was limited. In U.S. Pat. No. 5,190,635, a preferred process is described wherein the catalyst magnetic susceptibility and Curie temperature are controlled by processing conditions. In U.S. Pat. No. 5,985,134, a preferred separation temperature of up to 260° C. is stated. In U.S. Pat. Nos. 5,972,208 and 6,059,959, the optional use of a catalyst cooler is described to reduce the catalyst temperature from preferred regenerator temperature of about 700° C. to a cooled temperature of 38° C. to 260° C. Goolsby and Kowalczyk in EP 0951940 A2 disclose a preferred samarium/cobalt magnet to allow efficient operation up to 232° C. (450° F.) “without extensive cooling equipment”.
Another modern version of the catalyst separator has been developed by Nippon Oil Company. Ushio and co-workers in U.S. Pat. No. 4,359,379 that issued Nov. 16, 1982 describes magnetic separation of the catalyst using a Sala high gradient magnetic separator with a ferromagnetic matrix. As noted therein, the inventors note that the drum-type magnetic separator can remove iron dust, but is “useless” in separating the metal deposited catalyst. In some examples, air is used as a carrier fluid in the high gradient magnetic separator. There is no indication therein that the separations were made at high temperature, and one example shows operation at room temperature. Ino and co-workers in U.S. Pat. No. 5,520,797 that issued on May 28, 1996 also used a Sala high gradient magnetic separator with a ferromagnetic matrix and gas carrier. These devices have problems that limit their effectiveness and usefulness for magnetically separating hazardous dry powders.
The belt separator device can be enclosed in a pressure tight (or nearly pressure tight) containment vessel. Such a device is described in the U.S. Patents to Hettinger, Goolsby and co-workers. Such devices are presently marketed under the trade name of MagnaCat to separate fluidized catalytic cracker catalysts. The belt separator has certain disadvantages. Since the feed powder lies on a belt during the separation processing, particle-to-particle attraction forces interfere with the magnetic attraction forces. Therefore, particle cohesion and static electricity can make magnetic and non-magnetic particles stick to each other. When this happens, it is difficult to separate the particles into magnetic and non-magnetic streams. Another problem with such devices is belt wear. When the belt wears due to degradation, corrosion, abrasion or stretching, it must be replaced. This is especially difficult if the process is hazardous. In addition to natural particle attractions, the belt can actually increase particle-to-particle forces. Static electricity can build up on a rotating belt device, especially if the belt is a non-conducting elastomer. As indicated Supra, the belt separator can be enclosed in a containment vessel.
Another type of separator is the matrix/canister high gradient magnetic separator. Due to its matrix construction, this separator has intense local magnetic gradients that improve separation. By vibrating the device, particle-to-particle interactions are minimized. One method used to vibrate the device is to connect the canister with a flexible rubber boot around the full diameter of the canister. Such a rubber boot, however, is problematic with corrosive materials and hot, pressurized processing conditions. Operation of the device above ambient pressure is also difficult because the flexible boot tends to expand due to the internal pressure. This type of boot is also difficult to make reliable because it is as large as the diameter of the canister. For a twelve inch canister, the boot must be a minimum of twelve inches in diameter. The entire high gradient magnetic separator can be installed in a pressure tight container, but this adds to the capital expense of the equipment, and it adds to the complexity of maintenance operations.
The apparatus of the invention disclosed herein is a vibrating matrix, high gradient magnetic separator. It can process powders, vapors, liquids and gases that are corrosive, flammable or toxic. It permits operation at above ambient temperature and above ambient pressure. It is especially suitable for highly abrasive fine powders. It also provides for safe containment of process hazards.
The processes set forth herein are processes for manufacturing chlorosilanes.